Many portable recording devices are available with which a series of recordings may be obtained while travelling amongst several locations. Such devices are often able to associate with each recording a time stamp to indicate a time and date when that recording was obtained. The time stamps are usually derived from an on-board clock of the device.
It is usually incumbent upon the user to ensure that the on-board clock of a recording device is accurately set. Manually setting the on-board clock inherently involves inaccuracy stemming from human error, from the dexterity of the user, and/or from the reference time relied upon. Further, it is common for a user to simply neglect to change or set the on-board clock upon purchase of the device.
Similarly, it is common for a user to neglect to adjust the on-board clock upon movement to a different time zone, or upon seasonal time changes within a time zone. On-board clocks can also suffer from some amount of drift, which can become significant over time. Consequently the accuracy of an on-board clock, and in turn the accuracy of time stamps associated with recordings, often can not be considered to be reliable.
Separately to the preceding issues, a technique for associating locations with time stamped media such as digital photos has recently come about. This technique simply involves carrying a global positioning system (GPS) device along with a camera. The camera is used to record a series of photos each having an associated time stamp derived from an on-board clock. Meanwhile, the GPS device separately records a tracklog in the usual manner, the tracklog being a series of samples of location and time.
Subsequently, post-processing is performed to assign a location from the tracklog to each photo, based on corresponding timestamps. The time in GPS data can be considered to be trusted time data in such applications. However, the on-board clock in the user's camera is rarely synchronized to the GPS time. Such time discrepancies will lead to incorrectly assigned locations.
U.S. Pat. No. 6,690,883 provides for a self-annotating camera. The camera is operable to annotate a photograph with a number of types of data, including time data obtained from an on-board clock, and location data retrieved from an external GPS device. This camera must therefore be provided with sufficient capabilities to interface with an external GPS device. Further, once again the time data of the on-board clock can not be relied upon.
Other interfaces to align camera time to GPS time have proven to be prohibitively labor intensive and prone to error, and are thus inadequate solutions in consumer applications. One correction method allows the user to specify a time zone, which will generally correct the camera time by some integral number of hours. This method does not account for a camera clock that is wrong in minutes or seconds.
Another method allows the user to specify an arbitrary time offset. However, the user carries the burden of determining that time offset. One way is to simply look at the time displays in both devices simultaneously and calculate the difference. In addition to the inconvenience to the user of such arithmetic, this approach is problematic when one or both of the camera and GPS device do not show seconds, or if the camera clock has been reset or drifted after the photos were taken and before the alignment is attempted.
The user can also determine the arbitrary time offset by taking a photo of the GPS time display, thus capturing a photo that has a camera timestamp and a visual depiction of the GPS time in the single artefact. The time correction can then be carried out accurately in the future. Although more reliable, this still requires an amount of work that is prohibitive to most consumers.